It is often considered that As(III) and Cr(VI) can be converted to their following less poisonous forms As(V) and Cr(III) using several photo catalytic reactors. Does it mean that converted As(V) and Cr(III) can be consumed assuming that the water became safe for drinking ?If yes, what are their respective permissible concentrations for both new forms of these hazardous metals?
If not, how these new forms of As(V) and Cr(III) are removed for the safe drinking water?
Dear Brahm,
The toxicity of As is due to the element itself (not to its oxidation state). Therefore whether its present as arsenite As(III) or arsenate As(V) its irrelevant for the water and its not safe for drinking! Therefore In Europe, the Maximum Permissible Concentration in Drinking water is set to 10 ppb as As!
Dear Prof Svetlozar Velizarov,
Thank you very much for your prompt feedback.
Is there any reference to learn more about the technology adopted by Europeon Countries to keep the As limit in the permissible level?
I am keenly interested to learn more about the existing photocatalytic technology limits and possibilities to play a major role in water purification technology from As and Cr as a toxic metals as well as bacteria.
Warm regards,
Dear Brahm,
There are a number of possible technologies to remove As / Cr from contaminated water. The most widely used is chemical coagulation (FeCl3 or AlCl3 as coagulants), but there are also other possibilities like adsorption, membrane processes, etc. As to the possible membrane processes, you may look at a review paper I wrote some years ago.
Velizarov et al. Removal of inorganic anions from drinking water supplies by membrane bio/processes. Reviews in Environmental Science and Bio/Technology 3, 4, 361-380.
It´s available on my RG-page. Hope, this information will be helpful for you.
Best regards
Dear Prof Svetlozar Velizarov,
Thank you very much for your reference.
I would appreciate if some one could made any good comment on the following:
1. The photocatalytic technology converts As(III) and Cr(VI) into their so called less toxic forms As(V) and Cr(III), but according to Prof Svetlozar Velizarov toxicity will remain the same even after changing to their oxidation states, then why many researchers still want to work on the photocatalytic water purification technology?
2. If there are possibilities to improve the water purification using photo catalytic technology, What are the technological challanges regarding this technology?
3. If photocatalytic technology would not serve the water purification purpose from As, Cr, Dyes and bacteria etc, then can some one give any reference why proves/clerify such doubts?
Warm regards,
The As(III) and As(V) are different in their reactivity towards the enzyme present in the human body. As(III) binds the SULPHHYDRIL (-SH) group enzyme and blocks their further activity, while As(V) does not react at all. So the toxicity of both the species are different.
Dear Supriya Singh, Thank you very much for your comment. Does this mean that if As(III) is converted to As(V), which can be efficiently done using photo catalytic water treatment technology, it will help to solve the As contamination related health problem in various parts of world and especially, West Bengal, India? Warm regards, Brahm Pal Singh